1. Field of the Invention
The present invention relates to a self-dispersible bipyridine-based metal complex and an ink composition comprising the same. More particularly, the present invention relates to a bipyridine-based metal complex that may be efficiently dispersed even in the absence of a dispersing agent, and an ink composition comprising the same, wherein the ink composition has a desirable coloring property, durability, and dispersion stability.
2. Description of the Related Art
In general, colorants produce their specific colors by selectively absorbing or reflecting visible light, and are classified into dyes and pigments.
Dyes are substances that are used to color subject matters such as fibers, leathers, furs, and papers, and have considerable fastness to daylight washing, friction, and the like. Pigments are particles having color materials and are adhered to the surfaces of subject matters by physical means such as adhesion, instead of directly coloring the surfaces of the subject matters, producing their specific colors.
Dyes are used as colorants for foods, medicines, cosmetics, and ink-jet inks, in addition to the above-described fibers, leathers, furs, and papers. Pigments are used in paints, printing inks, plastic coloration, rubber coloration, furniture making, textile printing, paper making, ceramics, and the like.
Colors produced by these colorants are determined by which wavelength of visible light ranging from 3,000 to 7,000  the color material particles reflect or transmit. Based on such characteristics, colorants may be classified into two types, depending on molecular structures: organic colorants and inorganic colorants. Although coloration mechanisms are not clearly elucidated, for organic colorants, coloration is carried out by a cycle of light absorption, transmission, and emission through conjugation of double bonds. For inorganic colorants, when a ligand coordinating with a metal absorbs light, a ligand-metal complex is changed from an excited energy state to a ground energy state, thus emitting light, which produces colors.
Generally, organic colorants have wide coloring ranges and produce bright and clear colors, but have ineffective light resistance, such as decoloration or discoloration. On the other hand, inorganic colorants have excellent durability, including light resistance, but also have problems such as narrow coloring ranges and simple color types.
Hereto, various compound colorants have been known. Pigment metal complexes are disclosed in U.S. Pat. Nos. 3,971,739, 3,987,023, 4,077,953, 4,152,324, and Japanese Patent Laid-Open Publication No. 2001-152044. These patents disclose a method for preparing an azo compound-metal complex by a coordination bond and a covalent bond.
According to this method, however, there are restrictions in that a specific functional group of an azo group is required, and coexistence of functional groups for the coordination bond and the covalent bond requires appropriate spacing between the coordination bond and the covalent bond when the functional groups react with the metal. In addition, the above-disclosed complexes have an unsatisfactory durability and coloring property. Thus, there is a need for improvements.